1. Technical Field
The present invention relates to an organic light-emitting diode including a multi-layered electron transport layer and a flat display device including the same.
2. Description of Related Art
Organic light-emitting diodes (OLEDs) are self-emitting devices, and have advantages such as a wide viewing angle, good contrast, quick response times, high brightness, and good driving voltage characteristics. Also OLEDs can provide multicolored images.
In general, an OLED has a structure including a substrate, and an anode, a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and a cathode are sequentially stacked on the substrate. In this regard, the HTL, the EML, and the ETL are organic layers formed of organic compounds. When a voltage is applied between the anode and the cathode, holes injected from the anode move to the EML via the HTL, and electrons injected from the cathode move to the EML via the ETL. The holes and electrons recombine in the EML to generate excitons. When the excitons drop from the excited state to the ground state, light is emitted.
When the EML of the OLED includes a phosphorescent dopant, a hole blocking layer (HBL) may be formed on the EML to prevent triplet excitons or holes from being diffused into the ETL. The HBL is formed of a hole blocking material, and prevents holes from being diffused into the ETL, thereby enhancing the efficiency of the OLED. However, the driving voltage and lifetime of the OLED may be reduced.